Many medical investigations and surgical procedures are performed by endoscopic means today. Consequently the strain on a patient can be considerably reduced. However, because of the reduced visual field as a result of endoscopic access, endoscopic procedures require considerable practice on the part of the operator to make accurate estimates of the distance to a surface of an interior body cavity in which a surgical manipulation is to be performed. For the same reason, the measuring of internal body structures, such as ascertaining the size of a tumor, involves difficulties. Finally, the physician's difficulty in orientation in the interior body cavity, owing to the reduced visual field of an endoscope, can cause portions of the surface of the cavity to be overlooked in an endoscopic investigation, that is, not to be endoscopically collected. Therefore, for endoscopic diagnoses and procedures, the judging of distances and measuring of intracorporeal structures, like the spatial recording or reconstruction of an infernal body cavity, are of great significance. For this purpose, it is essential to collect 3D data on the cavity, and in particular to collect absolute 3D data that are based on an extracorporeal reference coordinate system.
Patent application DE 10 2006 017 003 A1 teaches an endoscope for depth acquisition in which a modulated light signal is emitted and the modulation parameters of the received light signal are used to compute the depth data. Via a plane semi-transparent mirror used as a beam splitter, beams can be received by two image sensors, one of which captures the modulation parameters useful for generating 3D data while the other is provided to capture a visual image of the endoscopic scene, in US 2006/0025692 A1, an endoscopic apparatus for generating an endoscopic fluorescence image is described, such that a distancing signal is generated by a distance-measuring unit, operating for example with ultrasound, microwaves or laser light. It is not possible with the aforementioned solutions to collect absolute 3D data, so that the recorded data are limited to the restricted visual field of the endoscope.
Patent application DE 10 2008 018 636 A1, which is incorporated by reference in the present application, teaches an apparatus for endoscopic 3D data collection, which includes light-generating means for generating at least a modulated measuring radiation, light-transmitting means for transmitting the measuring radiation onto an object to be observed and light-imaging means for imaging a signal radiation from an object to be observed onto a phase-sensitive image sensor. By evaluating the data provided by the phase-sensitive image sensor, 3D data on the observed object are generated. The collection of absolute 3D data is not foreseen by this apparatus.
Patent WO 94/03100 teaches a method for depicting the interior of bodies, where a spatial data field is associated with a body situated in a particularly position and the spatial position of a video camera, before which an endoscope is mounted, is recorded on a continuous basis, in addition, a depiction of a data field, which corresponds in each case to the current viewing angle of the video camera, is computed and the optical image and data field are simultaneously displayed on the monitor. By means of an input process by the user, one or more characteristic points of the data field are harmonized with the associated optical depiction on the screen. For the data field, it is possible to use a three-dimensional reconstruction, which is acquired from one or more previously shot video recordings, with which a distance measurement via ultrasound or by stereometric analysis is associated. The ultrasound distance measurement, however, allows the collection of only relatively few data points, while a stereometric analysis is restricted to high-contrast surfaces. Therefore, and because of the necessary interaction of the user, the usability of the method and the resulting advantages are restricted.
Patent DE 10 2004 08 164 B3, which is incorporated in the present application by reference, discloses an apparatus for producing at least a portion of a virtual 3D model of a bodily interior, said apparatus comprising an endoscope, a positioning system with an inertial sensing system to record the position and orientation of the endoscope, and a distance-measuring system to acquire at least one distance of the endoscope from at least one point on the surface of the bodily interior. Distance is measured with the help of a laser beam emitted by the endoscope on the basis of a triangulation or by run-time measurement of the laser beam or with the help of a pattern projected by the endoscope onto the surface of the bodily interior or else by ultrasound. From points on the surface of the bodily interior recorded by the distance-measuring system, a portion of a virtual model of the surface of the bodily interior is produced. Because this necessitates distance measurement from a number of different positions and orientations of the endoscope, only a relatively low spatial resolution can be achieved.
In an article by Höller et al. “Spatial orientation in translumenal surgery,” in Minimally invasive Therapy 19 (2010): 282-273, a flexible endoscope is described, on whose proximal end a time-of-flight (TOF) sensor is mounted. An inertial sensor is positioned at the distal end of the endoscope in order to establish the endoscopic image on a gravitational basis or to provide a corrected image horizon. However, an inertial sensor requires a relatively large structural area, and therefore cannot easily be integrated into a distal end portion, especially in flexible endoscopes with small diameter.